The present invention relates to coaxial cable connectors and, in particularly, to a coaxial cable connector having a helical duct-like inner conductor.
With the spread of the utilization of mobile communications, there have been more exacting demands for better-quality coaxial cables and coaxial cable connectors for use in antenna feeders of portable telephones, car telephones, and radio call system base stations.
FIG. 5 shows a typical partially cutaway cross-sectional view of a coaxial cable 400 known in the art (for example, WF-H50-13, a WF-H coaxial cable by MITSUBISHI CABLE INDUSTRIES, LTD.). On the other hand, FIG. 6 shows a typical partially cutaway cross-sectional view of a conventional connector 500 (for example, WF-H13D-BFX20D, a WF-H coaxial cable connector by MITSUBISHI CABLE INDUSTRIES, LTD.) for the coaxial cable 400. In these Figures, both the coaxial cable 400 and the connector 500 are shown substantially in their actual sizes.
As seen in FIG. 5, the coaxial cable 400 has an inner conductor 42, an outer conductor 44, an insulating body 46 interposed between the inner conductor 42 and the outer conductor 44, and a coating layer 48 for providing protection of the outer conductor 44. The inner conductor 42 and the outer conductor 44 are each formed by a corrugated duct. Typically, the outer conductor 44 is formed by a ring-like corrugated duct, whereas the inner conductor 42 is formed by a helical corrugated duct (also called the xe2x80x9chelical ductxe2x80x9d), as shown in FIG. 5. It is to be noted that the term xe2x80x9ccorrugated ductxe2x80x9d which has been used in the specification of the present invention includes both ring-like and helical corrugated ducts.
The inner conductor 42 in the form a helical duct (hereinafter also referred to as the helical duct 42) has a small diameter part 42a and a great diameter part 42b. An external thread is formed in an outside surface of the helical duct 42 at a fixed pitch and an internal thread is formed in an inside surface of the helical duct 42 at a fixed pitch. The inner conductor 42 and the outer conductor 44 are each formed by for example a copper duct. The insulating body 46 is made of for example low density expanded polyethylene, and the coating layer 48 (also called the xe2x80x9canti-corrosion layer) is made of polyethylene. Connectors of the present invention are capable of serving as a connector for the coaxial cable 400 (FIG. 5) and will be described by making reference also to FIG. 5.
Referring now to FIG. 6, the structure of the connector 500 will be described. For the sake of simplicity, an exemplary case, in which the connector 500 is mounted to the coaxial cable 400 (FIG. 5), will be described below.
The connector 500 of FIG. 6 has a center contact 50 which is electrically connected to the inner conductor 42 of the coaxial cable 400, a tubular body (body) 60 which is electrically connected to the outer conductor 44 of the coaxial cable 400 and which surrounds the center contact 50, an insulating member 70 by which the center contact 50 and the tubular body 60 are insulated electrically from each other.
The center contact 50 is roughly cylindrical and has a cable-side center contact 51 and an opening-side center contact 52. The cable-side center contact 51 and the opening-side center contact 52 are brought into mating engagement with each other in an area 50a, whereby they are connected together electrically.
The cable-side center contact 51, which is roughly cylindrical, has an external thread part 51a. The external thread part 51a is brought into mating engagement with the inside of the helical duct (the inner conductor) 42 of the coaxial cable 400. In other words, the external thread part 51a has an external thread formed at the same pitch as that of an internal thread formed in the inside surface of the helical duct 42. Further, in order to ensure that the cable-side center contact 51 and the helical duct 42 are connected together, a top-like member 54 inserted in the inside of the cable-side center contact 51 of roughly cylindrical shape is used to extend an end (a slot part) of the cable-side center contact 51 inserted within the helical duct 42. This makes utilization of a force exerted by tightening of a bolt 55a passing through the top-like member 54. More specifically, when the bolt 55a is tightened, the top-like member 54 is drawn toward the end of the helical duct 42 (the left-hand end in the Figure), thereby causing a tapered outside surface of the top-like member 54 to radially push and extend a tapered inside surface of the cable-side center contact 51. The degree of such extension can be controlled by adjusting the amount of tightening of the bolt 55a. When the bolt 55a is loosened, i.e., when the bolt 55a is turned left, the top 54 travels to the right (in the direction in which the top 54 comes off) while being in abutment with a stopper 53. If the bolt 55a is further rotated, this finally causes the top 54 to come off the bolt 55a. To prevent this, there is provided a nut 55b. 
The cable-side end of the opening-side center contact 52 has an outside surface in abutment with the inside surface of the cable-side center contact 51 and an end surface in abutment with the stopper 53. The outside surface of the opening-side center contact 52 in abutment with the inside surface of the cable-side center contact 51 has an external thread which is brought into mating engagement with an internal thread formed in the inside surface of the opening-side center contact 52. This mating area is the area 50a (FIG. 6). Defined in an opening-side end of the opening-side center contact 52 is a hollow part (hole) 52a. A center contact (a cylindrical projecting part) of another connector (not shown) is received in the hollow part 52a, whereby the inner conductors of the two coaxial cables to be connected together are connected together electrically. Further, a hole 52b is defined diametrally, passing through the center of the cylindrical opening-side center contact 52. The hole 52b can be used as an insertion hole through which a rod-like jig for rotating the opening-side center contact 52 is inserted, when the opening-side center contact 52 is threaded into the cable-side center contact 51.
The tubular body 60 has a first connecting tube 61 which is connected to the other connector (not shown) and a second connecting tube 62 which is, at its cable-side end, internally interfitted into the first connecting tube 61. A split clamp 63 is disposed within the second connecting tube 62. The split clamp 63, having an internal diameter and an internal surface shape conforming to an outer peripheral shape of the outer conductor 44 of the coaxial cable 400, is externally interfitted in the vicinity of a connecting end of the outer conductor 44. Further, an O ring 64 is disposed in the inside of the second connecting tube 62 so that the O ring 64 is brought into close contact with the coating layer 48 of the coaxial cable 400. The second connecting tube 62 is fixed, through the split clamp 63 and the O ring 64, to the coaxial cable 400 by application of pressure.
The first connecting tube 61 is externally interfitted to an end of the second connecting tube 62, and the first connecting tube 61 and the second connecting tube 62 are fixedly connected together at flanges 61a and 62a mounted on the first and second connecting tubes 61 and 62, respectively, by using for example a bolt. The end of the outer conductor 44 is located so as to be compressed and supported between the split clamp 63 and the first connecting tube 61 by virtue of force by which the first connecting tube 61 and the second connecting tube 62 are fixedly connected together, thereby further ensuring that the outer conductor 44 and the tubular body 60 (which is made up of the first connecting tube 61 and the second connecting tube 62) are brought into electrical connection with each other through the split clamp 63.
Further, the first connecting tube 61 has an inside surface in abutment with the outside surface of the annular insulating member 70 disposed around the center contact 50, and the relative position between the first connecting tube 61 and the center contact 50 is fixed through the insulating member 70. The first connecting tube 61 has, at the end opposite to the flange 61a, a flange 61b and is fixedly connected to the other connector (not shown) through the flange 61b by using for example a bolt (not shown), whereby the outer conductors of the two coaxial cables to be connected together are brought into electrical connection with each other.
However, the conventional connector 500 has the following problems. The center contact 50 of the connector 500 has a relatively complicated structure because of the cable-side center contact 51 and the opening-side center contact 52, thereby increasing production costs. Further, the step of mounting the center contact 50 is complicated, and in the step of extending the end (slot part) of the cable-side center contact 51 inserted within the helical duct 42, it is required that the degree of extension (the amount of tightening of the bolt 55a) be controlled adequately in order not to cause damage to the inner conductor. Furthermore, in some cases the opening-side center contact 52 and the cable-side center contact 51 undergo seizing to become unseparatable.
The present invention was made with a view to providing solutions to the above-described problems with the prior art techniques. Accordingly, an object of the present invention is to provide simple-structure, inexpensive, easy-to-mount coaxial cable connectors.
The present invention provides a connector which is mounted to an end of a coaxial cable having an outer conductor and an inner conductor formed of a corrugated duct insulated from the outer conductor. The connector of the present invention comprises: a center contact electrically connected to the inner conductor; a tubular body electrically connected to the outer conductor and surrounding the center contact; and an insulating member by which the center contact and the tubular body are insulated electrically from each other, wherein the center contact has an external thread part which is brought into mating engagement with the inner conductor, and wherein the external thread part has a first external thread of a first pitch shorter than a pitch of the corrugated duct.
The first external thread of the center contact may be brought into mating engagement with an inside surface of a small diameter part of the corrugated duct at the first pitch.
An arrangement may be made in which the corrugated duct of the inner conductor is a helical duct; the external thread part of the center contact further has a second external thread of a second pitch identical with a helical pitch of the helical duct; and the first external thread is formed in a great diameter part of the second external thread, and the second external thread is brought into mating engagement with the helical duct at the second pitch and the first external thread is brought into mating engagement with an inside surface of a great diameter part of the helical duct at the first pitch.
Preferably, the first external thread is brought into mating engagement with an inside surface of the inner conductor by self tapping.
Hereinafter, the operation of the present invention will be describe.
The connector of the present invention is provided with a center contact having an external thread the pitch of which is shorter than that of the corrugated duct constituting an inner conductor, and the external thread of the center contact is brought into mating engagement with the inner conductor. As the corrugated duct, either an annular corrugated duct or a helical corrugated duct may be used.
To those skilled in the art, forming threads in the inside surface of a duct whose inside diameter is not constant has been an inconceivable technical practice. This was examined by the inventor(s), and the results show that it is possible to provide sufficiently stable center contact/corrugated duct joining by threading a center contact having a first external thread of a first pitch into a corrugated duct having a pitch greater than the first pitch. Further, if a center contact is formed using a material harder than that of a corrugated duct, this not only eliminates the need for pre-formation of an internal thread in the inside surface of a corrugated duct but also makes it possible to form an internal thread in a corrugated duct by a self tapping technique using an external thread formed in the center contact. Accordingly, unlike the above-mentioned conventional technique, there is no need to carry out the step of extending a center contact end, and it is possible to form a center contact in the form of a single piece.
In the case inner conductors are formed of a helical duct, an external thread (a second external thread) of the same pitch as the helical pitch of the helical duct (i.e., a second pitch) is formed in a center contact and a first external thread of a first pitch (short pitch) is formed in a maximum diameter part of the second external thread. As a result of such arrangement, it is possible to bring the center contact and the helical duct into mating engagement with each other by both the first and second external threads. This provides more stable joining. Also in this structure, a corresponding internal thread to the first external thread can be formed in the inside surface of the helical duct by self tapping.